A medicine that is commonly used against parasites like tapeworms contains a substance that stops prostate and colon cancer cells from growing, a new study found.

The substance, called nitazoxanide, decomposes a protein called beta-catenin, which is required for increased cancer cell proliferation and survival, and is often involved in resistance to cancer treatments.

The study, “Small molecule promotes β-catenin citrullination and inhibits Wnt signaling in cancer,” was published in Nature Chemical Biology.

Cancer cells often acquire new features that are not normally found in healthy cells, allowing them to proliferate without restrictions and to survive for longer periods. In some cancers, overactivation of the Wnt/β-catenin signaling pathway is one of these features, making cancer cells two times more likely to develop resistance to treatment.

Now, researchers at the University of Bergen (UiB) in Norway found that the broad spectrum anti-parasitic and anti-viral drug nitazoxanide — which has been approved by the U.S. Food and Drug Administration since 2004 to treat diarrhea caused by Cryptosporidium parvum or Giardia lambliais — can efficiently block the Wnt/β-catenin pathway, making it a potential anti-cancer drug.

“We discovered that this specific substance is blocking the signaling pathway in the cancer cells, and make them stop growing,” Karl-Henning Kalland, professor at the Department of Clinical Science at UiB, and author of the study, said in the university’s news release.

“It is not often that researchers discover a substance that targets specific molecules as precisely as this one,” he added.

After testing 460 approved drugs, the team found that nitazoxanide specifically inhibits the activity of the enzyme PAD2, which in turn would promote the degradation of activated β-catenin protein in cancer cells. The findings suggest that in addition to nitazoxanide’s well-known anti-parasitic properties, the drug may be able to treat cancers in which the Wnt/β-catenin signaling pathway is overactivated.

“We are the first researchers who have mapped the complex molecular mechanisms involved in this process,” Kalland said.

Nitazoxanide is already known to be safe for humans, with no serious side effects associated to its use, “which means that a future treatment may happen quicker,” Kalland said.

While nitazoxanide affects cancer cells directly, it also appears to stimulate the immune system. The UiB research team is now evaluating how nitazoxanide affects the immune response against cancer cells.